Foundry composition



Sept 23, 1941. N. J. .DUNBECK 2,256,943

FOUNDRY COMPOSITION Filed March 10, 1941 Patented Sept. 23, 194i FoUNDaYooMrosrrroN Norman J. Dunbeck, Eifort, Ohio, assignor to PeerpatcoIncorporated, a corporation of Delaware Application March 10, 1941,Serial No. 382,656

9 Claims.

My invention relates to compositions of matter, and more especially tosuch compositions as are used for foundry binders and to the foundrycompositions employing such binders.

One of the objects of my invention is the provision of a bonding agentwhich is made from inexpensive and readily available materials and whichcan be so modified that numerous types of foundry work are performedwith good results by its use. y

Another object of my invention is the provision of a'foundry compositionwhich has adequate strength yet is of sufficient permeability underworking conditions to allow the escape of gas and fumes, which at hightemperatures is capable of withstanding the cutting and washing effectsof the casting material, which at approximately 2000 F. has peak hotstrength, which, at the same time, has an unusually high green strengthtogether with a high sinteringpoint and which resists caking andhardening in use, which is easily recovered after use and which may berepeatedly employed to give sound, high grade castings.

A further object of my invention, along with those previously mentioned,is to provide a foundry composition the proportions of the ingredientsof which are capable of being preselected to produce a desired hotstrength of composition to meet instant working requirements and whichhas satisfactory hot strength without the sacrice of other desirablequalities necessarily present in a molding composition.

Other objects i part will be obvious and in part pointed outlereinafter.

The invention accordingly consists of the combination of elements,mixture of materials and` composition of ingredients and in the severalsteps and the relation of each ,of the same to one.or more of the othersas described herein, the scope of the application of which is indicatedin the following claims.

The accompanying drawing compares the change in hot strength of a moldcomposition made in accordance with my invention, with the change in hotstrength of a conventional mold composition; based upon the change inthe proportions of the ingredients contained in the bonding agent.

In forming foundry compositions it is common practice to thoroughly mixwith clean silica sand a proportionately small amount of clay binder andthis mixture when tempered with water forms a workable molding material.The prac- As a general rule, it is desirable to maintain the watercontent of a foundry composition reasonably in keeping with thecharacteristic permeability of the mixture. When this is done, lesssteam will be formed, and that which is formed, will have an opportunityto escape from the mold, with the result that the danger of having gasaws appear in the casting is consequently reduced. Too little moisture,on the other hand, is likely to produce a composition of undesirabledryness, and in consequence, the mold will crumble or wash duringfoundry operations. Harder ramming could be used to overcome excessdryness except for the fact that such practice materially reducesthepermeability of the composition. Thus it is to be observed that intaking steps to correct one existing fault in a mold composition, othernew and undesirable factors are likely to arise unless particular careis exercised in originally selecting proper constituents for the foundrycomposition.

The amount of clay mixed with a molding sand should be low in proportionto the quantity of sand. The type of molding sand available has agoverning effect upon the amount of bonding material needed. Forexample, an angular or sub-angular grained sand requires less clay thana sand having smooth rounded grains. Fine grained sands require lessclay bonding agent' than do coarse sands. Ordinarily the amount ofbonding clay employed, ranges from 5% to 30% of the mass of the moldmixture.

Several types of bonding clays are now used in foundry practice.Probably the most prevalent among these clays are the re clays which arelargely comprised of kaolinite and naturally included montmorilloniteand beidellite. Nonrefractory clays are also employed and they aregenerally of glacial origin and are predominant in minerals of thesericite or illite type. Certain sedimentary clays of greater geologicalage are also found in the non-refractory group. A large proportion ofthe mineral beidellite or illite may also be found in these clays.

Both refractory and non-refractory clays can be obtained from variousparts of the United States. Such clays have not proven to be highlysatisfactory, however, since they fail to give necessary mold strengthwhen .used in small amounts. When the percentage of such clays isincreased in foundry compositions, the mold permeability is thenseverely decreased and mold tice of substituting burnt or reclaimed sandfor dry strength'is unduly increased. It is highly essential that afoundry composition be sufficiently permeable, otherwise the necessaryescape of gas and fumes generated at working temperatures is impaired.If too much clay is used, the mold will bake hard at workingtemperatures. Castings will crack when a part of the mold which ispartially surrounded by metal bakes so hard as not to allow the castingto shrink properly as it cools. It is accordingly, obvious that a highamount of clay present in a molding composition is undesirable.

Where a clay, such as fire clay, is employed as the bonding material,the amount required varies from approximately to 30% of the mass of themolding sand, depending upon the quality of the sand` and upon thequality of the clay. Clay of this sort lends good hot strength to amolding sand, but at the same time impairs the permeability of the sandand imparts an undesirably high dry strength to the sand. For reasonssuch as the latter, the use of fire clay for a foundry bonding agent isrestricted.

Good green strength of mold together with good permeability anddesirable dry strength can be obtained by using either a non-swelling,colloidal or non-colloidal clay binder. The properties of a PortersCreek clay binder, a nonswelling, non-colloidal clay, are more fullydescribed in my Patent No. 2,128,404, issued to me on August 30, 1938.The adaptability for foundry use of a non-swelling, colloidal clay ofthe Pontotoc, Mississippi type, is set out in my Patent No. 2,180,897,issued to me on November 21, 1939. 'I'hese non-swelling clay bindershaveproven to be quite satisfactory in most respects except that theyare not totally satisfactory for high temperature work since they tendto impart low hot strength to molds at high temperatures.

Swelling montmorillonite or Wyoming type bentonite binders have manyadvantages in foundry practice, but one disadvantage which has beenrecognized by foundrymen is the exceptionally high dry strength obtainedby the use of such binders. This latter characteristic causes diflicultywhen the molding material is removed from the ask. The material bakes togreat hardness. To shake the mold from the ask'is expensive since theflasks must receive rough treatment. More expense is encountered in thatmuch of the baked sand cannot be reclaimed for it is dicult to crushfrom hard lumpy condition. Further, Wyoming type bentonite is expensiveto obtain in the eastern part of the country because of the greatshipping costs involved.

Another problem which arises in foundry practice ls that of obtaining abonding agent for use in foundry sands which can be suited to difierentworking conditions without changing more than the proportion of itsbasic ingredients. Castings of different sizes and proportions and ofdiering materials can be produced conveniently when a bonding agent ofthis nature is employed. The ingredients of the bonding agent can be somodified in proportion that the particular working requirements will besatisfied. A procedure such as this is by far more economical than thatof using an entirely different bonding agent each time a different typeof casting is to be produced.

Some compositions, such as those in which Wyoming type bentonite bondingagent is used, are very satisfactory when heavy castings are made, sincein this instance, a higher dry strength of the composition i.'permissible. On

the other hand, compositions containing a Wyoming bentonite binder havea dry strength too great to be satisfactory for use in casting smallthin objects. A non-Swelling montmorillonite whether a non-colloidalclay such as Porters Creek clay, as described in my Patent 2,128,404,above referred to, or a colloidal clay as set forth in my Patent No.2,180,897, also referred to above, are suitable for use as bondingagents in the production of thin, light castings, for they impart arelatively low dry strength to compositions in which they areingredients.

It was subsequently learned that the constivtuent parts of a moldbonding agent can be varied in proportions so as to impart to moldingsands with which the agent is mixed, any desired, pre-determined drystrength. This development is set out in my Patent No. 2,230,939, issuedto me on February 4, 1941, which discloses a foundry composition havinga bonding agent basically comprised of Wyoming type bentonite and anon-swelling montmorillonite. A valuable advantage of a binder formedwith these constituents lies in the fact that the dry strength of moldin which it is employed definitely can be pre-determined by properproportionment of basic binder ingredients. Consequently, the foundrymanis furnished with a new and valuable method of controlling mold drystrength. Once the particular working conditions are known, the drystrength of the mold composition can be designed to meet the instantneeds. This is accomplished by mixing together the proper amounts ofbonding ingredients and sand. Fortunately, many other advantages followfrom the above improvement. The danger of having sand bake in the asksbecause of the presence of an excess of clay has been overcome. It is asimple matter to break down the dry composition and thereafter recoverthe burnt sand without encountering hard lumps.

One puzzling factor which has become evident while controlling the drystrength of foundry compositions by the practice of properlyproportioning the constituents of the binding agent, is that of thedevelopment of cuts and washes in the mold and in the casting at hightemperatures. This occurs in spite of the fact that the dry strength ofthe foundry composition is carefully regulated. Precise control over drystrength of a foundry composition does not, in the same measure, giveabsolute assurance that the hot strength of the composition will besuitable. Therefore, even though the molding material does not bake to ahard degree, and even through it is easily removed from the flask,recovered and reconditioned, the casting itself may still have scabs,iiaws or defects because of the cutting and washing away of portions ofthe mold composition at high temperatures. This condition is more orless prevalent depending, for example,

-upon the working temperatures; the nature of the casting, as forexample, the character of the casting material; the composition of thefoundry material with respect to proportion of elements. one totheother, of sand, moistening agent and bonding material or to theproportions, with respect to each other, of the elements of which thebonding agent is comprised.

It will be observed from Table I that a foundry sand containing bondingmaterial of the combined Wyoming bentonite (B) and non-swellingmontmorillonite type (M), as described in my previously mentioned PatentNo. 2,230,939, does not possess extremely high hot strength in theneighborhood of 2000 F., but has reached peak hot strength near 1500 F.

Table I Bond M 75% M 50% M 25% M B 25% B 50% B 75% B Percent bond 4 3. 84. 3 4.8 5 Percent moisture 2.6 2. 5 2. 5 2. 5 2. Green compression (p.s. i.).. 9. 9 9. 6 9.8 9. 8 9. Dry compression (p. i. 47.0 42.0 59.059.0 83.

Hot strength (p. s. i.)'

c] M)=Nonswelling colloidal montmorillonite (Pontotoc MississippiB=Swe1ling montmorillonite (Wyoming type bentonite).

Accordingly the main object of my invention is to provide a bondingmaterial which imparts good high temperature hot strength to moldingsands, which contains cheap and readily available ingredients, which haspeak hot bonding strength at temperatures around 2000 F., which has ahot bonding strength that is capable of being predetermined by properproportionment l of binder constituents, which imparts high greenstrength and an adequately high dry strength to molding sands regardlessof the proportions of the bonding material constituents used and whichhas good permeability and good workability, together with a highsintering point.

Considering now the practice of my invention, I prepare my bondingcomposition by thoroughly mixing kaolinite (K) with another claycomposed largely of non-swelling montmorillonite (M). My invention isnot to be limited in any way to the combination of these particularingredients, but such ingredients are to be treated as illustrativeonly. The non-swelling montmorillonite clay which I use can be, forexample, either of a colloidal or non-colloidal nature. I control thehigh temperature bonding strength of my foundry binder by varying therelative amounts of kaolinite and montmorillonite placed in the mixture.By increasing the amount of kaolinite in my composition I iind that thehigh temperature bonding strength of the binder will improve. Green bondstrength is unusually high in such kaolinite and montmorillonite bindercompositions, hot bond strength is ideal and dry bond strength issufficiently low. Further, the materials which I use in my bonding agentare cheap and readily available in many parts of the country, such as inthe eastern States.

In preparing a foundry mold composition in accordance with oneembodiment of my invention, I form my foundry binder of kaolinite (Ohioiire clay) and non-swelling, colloidal montmorillonite (Pontotoc,Miss.). The two ingredients are mixed to produce a uniform mass.Thereafter, I add by weight to approximately 85% to 98% of clean silicasand or silica sand containing a certain proportion of burnt sand asdesired, 15% to 2% of my binder comprising kaolinite and non-swellingcolloidal montmorillonite. The whole is then mixed in the usual foundrymixers to obtain uniform consistency. Thereafter, water is added indesired amount, usually 2% to 5% by weight. The mixing is thencontinued, nally giving a homogeneous mixture of desired strength andworkability.

accurately by proper proportionment of the parts of kaolinite (K) andnon-swelling montmorillonite (M). It is to be observed from Table II andin the drawing that for a given temperature the hot strength of afoundry sand containing my bonding agent increases fairly uniformly asthe percentage of kaolinite in the bonding agent is increased.

It will also be observed that the experimental results given in Table IIare based on tests made on foundry compositions containing variedproportions of kaolinite (Ohio fire clay) and montmorillonite of thePontotoc, Miss. type.

Table II Bond M M 50% M 25% M K 25% K 50% K 75% K Percent bond 4 5 6. 59. 25 l2 Percent moisture 2. 6 2. 6 3. 2 3. 7 4. 0 Green compression (p.s. i.) 9.9 12.9 10. 4 11.0 8. 5 Dry compression (p. s. 47.0 55. 0 71. 083. 0 71. 5 Hot strength (p. s. i.):

M=Nonswelling colloidal montmorillonite.

K=Kaolinite.

It is to be especially noted when comparing Table I and Table 1I thatthe hot strengths of mold compositions which contain bonding materialscomprising proportionate parts of kaolinite and non-swellingmontmorillonite clay are very high in the neighborhood of 2000 F. whilethe hot strengths of bonding materials comprising Wyoming bentonite andnon-swelling montmorillonite clay have begun to decrease aftertemperatures higher than 1500 F., are reached. It is accordingly,evident that the present invention permits the foundryman to producebetter castings at high temperatures.

Further, by the practice of my invention the likelihood of obtainingcracked castings because of excess hot strength of mold is eliminated.While suilicient hot strength of a mold composition is necessary toprevent the casting material from cutting and washing into the mold, itis also essential that this strength be not too great. The hot strengthof a mold composition must not be too high, or metal sections whichpartially enclose mold material may crack because the sand does not havesuiiicient collapsibility to permit normal metal shrinkage. I haveovercome this diiculty by providing bonding elements which can becombined in such proportions that a predetermined hot bond strength at agiven working temperature can be obtained. Therefore, in a foundrycomposition containing my bonding agent, the hot strength of thecomposition for a given working temperature can be modified by changingthe'proportions of the ingredients in my bonding agent. Thus, once theworking temperature is known, I prepare' a mold composition comprisingsand, kaolinite and nonswelling montmorillonite in such proportions, oneto the other, that the hot strength o! the composition will not be toohigh, nor too low. By the use of a molding composition prepared in thismanner, there is little danger that its hot strength will be so greatthat the casting mold composition will not be so low that molten The hotstrength of such mixture is controlled 75 casting material will wash, orcut into it. Con,

sequently, clean, sound castings can be produced at high temperatures,free from cracks, cuts, and scabs. No sand will cut or wash from themold composition, to be replaced by metal washes and mix with thecasting material to cause an imperfect casting to be produced. Mybinder, therefore, is economical in use, for it enables consistentlygood castings to be produced at high temperatures with a minimum wasteof labor, time, and materials.

The ingredients going to make up my mold composition may be mixedtogether in any desired sequence. While the amount of mixed kaoliniteand non-swelling montmorillonite bonding material is illustrativelygiven as about 2% to 15% of the weight of the sand with which it isincorporated, it will be noted that these amounts may vary beyond thegiven limits, depending upon the nature of the sand which the foundrymanmay ydesire to use. In fact, these amounts will change considerably ifburnt or reclaimed sand is chosen, since much bonding material may bepresent in the reclaimed sand. requiring an addition of only a fewtenths of a percent of mixed kaolinite and non-swelling montmorilloniteto restore original strength. In foundries which have only a slightdaily loss of sand on the castings, it is frequently desirable to make ahighly concentrated mixture of sand and blended bond clays, the clays insuch cases sometimes comprising 50% of the mixture. Only a very smallamount of such concentrated strength sand will be added to the moldmaterial which it is desired to strength.

Although, as illustrative of my invention, a green mold compositioncomprising silica sand and a combination of kaolinite and a non-swellingmontmorillonite has been stressed, my invention is applicable to likecombinations of sand and clay for other foundry uses.' These include thepreparation of cores and both green and dry and facing sands. Any ofthese may consist of new silica sand, burnt silica sand, new moldingsand, burnt molding sand, lake sand or bank sand, together with thebonding material to which may be added auxiliary binders in smallquantities, such as cereal binders, goulac, cement, pitch or rosin, or acasting cleaning element such as sea coal, wood flour or oils. In thepractice methods in common use.

As many possible embodiments may be made of my invention and, as manychanges may be made in the embodiments hereinbefore set forth, it is tobe understood that all matter described and illustrated herein is to beinterpreted illustratively and not in a limiting sense.

I claim:

1. In a composition of matter, a foundry composition comprising incombination, sand, kaolinite and a clay of which montmorillonite is alarge constituent.

2. In a composition of matter a foundry composition comprising incombination silica sand, kaolinite and a non-swelling, non-colloidalclay largely comprising montmorillonite.

3. In a composition of matter, a foundry composition comprising incombination silica sand, kaolinite, and a non-swelling, colloidal claylargely comprising montmorillonite.

4. In a composition of matter, a foundry composition comprising incombination silica sand and 2 to 15 percent of a mixture of kaoliniteand montmorillonite.

5. In a composition of matter, a foundry mold composition comprising incombination silica sand and a mixture of kaolinite and non-swellingmontmorillonite in such proportions as lto give a desired hot strengthof mold.

6. In preparing a mold for foundry purposes, the art which includesmixing with silica sand a binding material comprising kaolinite andnonswelling montmorillonite in such relative proportions as to produce adesired hot strength of the mold.

7. A foundry binder comprising kaolinite and a non-swellingmontmorillonite clay.

8. A foundry binder comprising kaolinite and a non-swelling colloidalmontmorillonite clay.

9. A foundry binder comprising kaolinite and a non-swelling,non-colloidal montmorillonite clay.

NORMAN J. DUNBECK.

